Wave guide mode transformer



April 6,1948. R. E. CLAPP WAVE GUIDE MODE TRANSFORMER Filed Aug. 1, 1945 QNQE Wm 1. mm

INVENTOR ROGER E. GLAPP ATTORNEY fatented Apr. 6,

NITED STATES PATENT OFFICE WAVE GUIDE MQDE TRANSFORMER Roger E. Clapp, East Cambridge, Mass., assignor, by mesne assignments, to the United States of America as represented by the Secretary of War Application August I, 1945, Serial No. 608,316

Claims. 1

This invention relates to electrical apparatus and more particularly to apparatus for transmitting electrical energy.

It is well known in the art that electrical energy may be transmitted through a wave guide in several diiferent modesor configurations of the electric and magnetic field. It is also known that the efiiciency of transmission of the electrical energy is different for the difierent modes. It is often the case, however, that the most efiicient mode is diificult to excite without exciting other undesirable modes Within the wave guide] The expedient usually resorted to in eliminating these undesired modes is to excite the dominant mode in a wave guide that is small enough to eliminate all higher .modes. A mode transformer is then employed to change from the dominant mode to the desired mode.

It is an object of thepresent invention, therefore, to present a novel mode transformer so designed that all undesirable modes are eliminated.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings in which: I

Fig. l is an isometric view of the invention;

Figs. 2 to 17, inclusive, are a series of sectional views of the deviceshown in Fig. 1 taken perpendicular to the main axis of the mode transformer at the lines 2-2 to ll-Il respectively;

Fig. '18 is a viewof the method of transition from a cross shaped wave guide to a circular wave guide employed in Fig. 1; l l

. Fig. 19 illustrates a second method of making a transition from a cross to a circular wave guide;

Fig. 20 shows a third method of making the transition from a. wave guide in the shape of a cross to a circular wave guide; I

Fig. 21 shows a. rectangular wave guide excited in the dominant or the TEo,1 rectangular mode The TEo,1 rectangularmode is the dominant mode in a rectangular wave guide and the TEo,1 circular mode is a modeiwhich has very low attenuation characteristics. The undesirable TE2,1

2 mode may be propagated in a circular wave guide that will propagate the 'I'Eo,1 circular mode.

Th mode transformer shown in Fig. 1 consists of seven transition sections in series so that a gradual transition is made from a rectangular wave guide In to a circular wave guid l2.

In the first transition section included between the lines 2-2 and 44 of Fig. 1 the shorter dimension of the rectangular wave guide I0 is gradually increased until it is twice its original length. A dividing section I4 is gradually introduced into the wave guide as shown in Fig. 3 until in Fig. 4 the single wave guide Ii] in Fig. 2 has been divided into two identical wave guides l6 and I8 in Fig. 4. The second transition section is included between the lines 4-4 and 6-6, In this transition section thelonger axes of both wave guides l6 and I8 are gradually rotated through 90 until the two wave guides are in the position shown in Fig. 6. The third transition section is very similar to the first transition section. It could be made up of two of the first transition sections placed side by side so that the two wave guides l6 and I8 at, lines 6-4 are graduallychanged to form four wave guides 20, 2|, 22 and 23 as shown at line 88. In the transition section included between the lines 88 and l.0l0 the longer axes of the four waveguides 20 to 23 inclusive are gradually rotated from the position shown in Fig. 8 through until they are in a position shown in Fig. 10. At line |0,l0 a hollow squareZB (see Fig. 10) is formed by the shorter sides of the four wave guides where they join. The fifth transition consists of gradually deforming the sides of the wave guide that form this square until at line i2 thespace between the wave guides is entirely eliminated as shown in Fig. 12. In a transition made from line I2-I2 to line |4-|4 the dividing walls 28 between the four wave guides are gradually removed until;at line Ml4 the transformer has the shape-of a hollow cross as illustrated by Fig. 14. The final transition from the shape of the hollow cross is made as shown in Figs. 15 and 16 until at line l'l-Il the circular shape is obtained. The transition between lines I l-I4 and I i-l1 is more clearly shown in Fig. 18. The solid line 30 in Fig.- 18 represents the cross-section of the wave guide of Fig. l in the vicinity of line l4--l4. The dotted lines 32 represent successive cross-sections of the wave guide going from line 14- to line |'|-l1. Only two quadrants of the transition are shown. It can be seen. from Fig. 18 that the sides 34, 3 B, 38 and 4B of the transformer are moved gradually outward parallel to themselves until the circular shape is obtained. A second form of transition that might be employed to go from the cross shape to the circular wave guide is shown in Fig. 19. In this type of transition the adjacent sides Q2 and 44, and 46 and 48 of the transformer are gradually bent outward as indicated by the dotted lines 50 until the circular shape is obtained. The third 'type oi transition illustrated in Fig. 20 is to expandth dimension of each of the four ends of the cross while maintaining the dimen;-

sions at the center of the cross constant until' a circular wave guide divided into, four quadrants by a thin dividing wall is obtained as illustrated by the single dotted line 52 inthe twoquadran'ts of Fig. 20. These dividing I'walls 52 a're graduallyreduced until the circular shape is obtained." If this third type of transition is used, the elimination of the dividing section 28 shown in Fig; 12

other cross-section.isflsubstantiallyethe same so.

that no. phase shift ,a between. the .vectors. in. any cross=section is.;pr'oduced..byr different electrical lengths; that .tlie..energy;mustitravel;

Figs. 2 to siillustratehow: theelectriafieldrepresentedtby the single arrow at line.2-.'2 is.grad-. ually dividedinto twofieldsiniphase ateline da l. These two .fieldslare .then changed; until they. are 180?. .outofiphasejin. space at Benefit-"6 while they are still. in phase intimel. 'Atvline'.8 '8;the. orig-f of these fieldsare in phasewi'th the original. field andtwo are 180space".degrees;out of phase with the. original -,fie1d;: At lin'e 8 8 the -four-Lfields have beenfr'otated so that'ieachtfieldis 90 out of phase in space .tothe field: in: .the adjacentwave how the four filds' atline l 4.l-4- aregraduallyshaped into the circular electric field at line-11 in It canbe seen that the chanse in theelectrio field from line 14 tosiigie 1 1 -11 will be essenti'allythe same regardless of the type' of transition used. 1

'It canbe seen fr-om the above description that f W 3 erl e dies he. the transformer o by in d cing suitable pdaric'e transformers bet sections of rectan ular wave guide if -d es ired, but in general the she erthe'physicallength of the transformer the'l times gnai2;wi1i}be1aitehuated'in'passing throiigl'iiit; v A

This mode transformer'inay also be used to transform energy from the" TEO, 1 circular mode to the TE6,1 rectangular rfiode. In this case the this'tians'forifii' chan es the e ect ica e erg imensions of j l ll s i im Itshouldbe e'i i ha ii ij 91 s lf siiiqn' 599-? tions may be connected: together with-- straight electric field configuration within each cross section will be substantiall the same as that shown in the drawings except that they will ocour in reverse order. Advantages of this device may be summarized as follows. The TEo,1 rectangular mode is transformed to the TEo,1 circular mode with a minimum of interference from other modes. This deyigeeinploys no mode filters so any loss from such devicesis thereby eliminated. The device is bilateral, and, therefore, may be used to transform energy traveling in either directionirom a circular to a rectangular waveguidef and the device may be constructed in sectionsiif desired; to facilitate the manufacr iiiisiiie mneii While there has been described what is at present consideredjhe preferred embodiment of the invention, it will be obvious to those skilled in the'artthat various changes and modifications may be made therein without departing from the invention.

What is .claimed'is;

1. A mode transformer comprising atleast-six serially. connected transition sections, the firstiof said transition sections .providing. means whereby one wave-guide zmaybeiconnected to two similar waveguides, a second .ofis'aid transition-sections providing means whereby-.the. axes .of two. wave guides maybe. rotated :91)? in space, thetthird of said- .transition sections providing means .whereby two-similarw aveguides maybeconnectedto-four other similar wave guides; thefourth of: saidtransition. sections. providing. means. wherebythe axes 'ot-Iour .wave. guides beiotated-througlr 45 in space, the fiftheof sai'dztransition sections providing. means whereby. four. wave. guides .Imay be connected to a Sing-EQWELVG guide having the form of a cross,- and theisixth-eoi .saidr transition sections providing-meanswhereby a wave. guide in a form. ofla cross may be connectedto a circular wave ..guide.-

2. A method of changing the mode of transtwo'other paths, rotating the configuration of-the electrical =fleld vectorsin the -dour paths thus formed. through: 45 degrees in space and combiningtheenergy from: said iourlast-mentionedpaths into a circular wave' 'guidewwhereby-the,

TEo' i mode is excited. in the circular wave guide.

' 3.2 A. methods-0fchangi-ng-i the .mode of transmission. .ofizelectnical energy-from the TE rectangularwmode vto =the-TEM- ci-rcular mode iiiclud ing the steps of exciting. a..rectangular wave-guide in" the .TEo,i mode;- dividing the electrical energy equally into ;n.paths rotatingintspacethe electricfield configuration in theil first path by ifi i V d e rotatine.tinrspace.th electric: fi ld r0011- fi uration-in thesecondtpathby.

le fii-m ii in -gl e ag n -electric flea-. gra iqg ethe r li P. byieeiamquet where r includes all integers from 3 to 11. both inelusive, and recombining the energy in said n paths in a. circular Waveguide.

4. In a waveguide transmission system including a rectangular waveguide and a circular wave guide, a mode transformer comprising at least six transition sections, the first of said sections providing means whereby one rectangular waveguide may be connected to two similar waveguides, means joining a first end of said first section to said rectangular waveguide, the second of said sections providing means whereby the axis of two rectangular waveguides may be rotated 90 in space, means joining a first end of said second section to the second end of said first section, the third of said sections providing means whereby two rectangular waveguides may be connected to four similar wave guides, means joining a second end of said second section to a first end of said third section, the fourth of said sections providing means whereby the axes of four waveguides may be rotated through 45 in space, means joining a first end of said fourth section to a second end of said third section, the fifth of said sections providing means whereby four rectangular waveuides may be connected to a single waveguide having the form of a cross, means joining a second end of said fourth section to a first end of said fifth section, the sixth of said sections providing means whereby a waveguide in the form of a cross may be connected to a circular waveguide, means joining a second end of said fifth section to a first end of said sixth section and means joining a second end of said sixth section first end thereof of a rectangular waveguide and having a shape at the second end thereof of two rectangular waveguides with a common broad wall, said second section having a shape at the first end thereof that is identical to the shape of said second end of said first section and having a shape at the second end thereof of two rectangular waveguides having a narrow wall in common, said third section having .a shape at the first end thereof identical with the shape of said second end of said second section and having a shape at the second end thereof of four rectangular waveguides arranged in a square with two broad Walls in common and two narrow walls in common, said fourth section having a shape at the first end thereof identical with said second end of said third section and having a shape at the second end thereof of four waveguides arranged in the form of a cross with one narrow wall of each waveguide forming the walls of a square at the center of said cross, said fifth sec tion having a shape at the first end thereof identical in shape to said second end of said fourth section and having a shape at the second end in the form of a hollow cross, and said sixth section having shape at the first end thereof identical with the shape of said second end of said fifth section and having a shape at the second end thereof of a circle.

ROGER E. CLAPP.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,129,669 Bowen Sept. 13, 1938 2,129,714 Southworth Sept. 13, 1938 2,253,503 Bowen Aug. 26, 1941 2,401,751 Friis June 11, 1946 

